The invention relates generally to the chemical vapor deposition (CVD) of platinum group metals on an integrated circuit structure as a continuous film and with good step coverage. The invention also relates to integrated circuits having a platinum group metal layer, used, for example, as the lower electrode in a capacitor.
Because of their high corrosion resistance, microelectronic devices having platinum group metals are desired in applications where great reliability is desired and also where a corrosive atmosphere may be present. It is desired to so develop a process for continuous good step coverage using platinum group metals.
The invention relates to the formation of a continuous film layer of platinum group metal by CVD. The invention may find many uses where a thin uniform layer of platinum group metal is needed. For example, the invention is useful in the computer microchip industry, such as for the undercoating electrode of a dielectric memory in a semiconductor device. The invention relates to a chemical vapor deposition method to deposit the platinum group metal onto a surface. The starting material for preparation of the platinum group metal film may be any organic platinum group metal precursor suitable for deposition of the platinum group metal.
Unfortunately, the conventional methods of depositing platinum films suffer drawbacks in that these methods are unable to consistently create a continuous uniformly thin platinum film that additionally has good step coverage. These conventional prior methods include vacuum deposition methods, sputtering methods and even chemical vapor deposition. Even in the conventional chemical vapor deposition methods it is difficult to create a continuous uniform platinum film and one with good step coverage.
This is likely due to the fact that when conventional platinum precursors are used in the conventional chemical vapor deposition methods, it is difficult to control the nucleation rate of the platinum films. At the outset of the platinum deposition process, the nucleation rate of the platinum film onto the surface of the substrate is very slow; however, once nucleation does begin the deposition rate of the platinum film onto the surface increases significantly. In fact, it is difficult to control or even slow the rate of deposition once the conventional methods begin depositing platinum onto the surface of the substrate. In the conventional methods therefore, it is difficult to begin the deposition process and even more difficult to control the deposition rate so as to arrive at a uniform thin platinum film having good step coverage.
In semiconductor processing, controlling the rate of deposition of a film is one important characteristic to a processing method. The conventional platinum deposition methods are unable to consistently control the deposition rate of the platinum film so as to consistently arrive at a platinum film that has sufficient physical properties to be useful in integrated circuits.
One example of the use of a platinum metal according to the conventional methods is discussed with reference to FIG. 12. A platinum layer 210 is deposited onto the surfaces of a deep container capacitor 200. The platinum layer 210 is formed by CVD deposition using a conventional platinum precursor. As the process begins, a platinum film 210 forms on the upper layer 220 of the capacitor 200. Since it is difficult to control the deposition rate of the platinum layer 210, the platinum layer 210 quickly forms a thick layer on the upper layer 220 of the capacitor 200. As a result, the quickly formed platinum layer 210 pinches together over the opening 230 in the capacitor 200 and very little platinum is able to form on the inside walls 240 or the bottom 250 of the capacitor 200. Thus, in this process, an inconsistent platinum film is formed on the inside walls 240 and the bottom 250 of the capacitor 200 without good step coverage.
One prior solution to increase the smoothness of the film deposited was to increase the temperature at which the metal is deposited. When the temperature at which the conventional CVD process operates is increased, the growth rate of the platinum also increases. While increasing the temperature does result in a smoother film, the increased temperature also increases the deposition rate, resulting in poor step coverage, as previously described. If the temperature of the CVD process is decreased, the growth rate of the platinum also decreases, resulting in better step coverage; however, when the temperature of the CVD process is decreased the carbon content of the film increases, resulting in poor film quality.
To reduce the carbon content of the film, the conventional methods added oxygen to the CVD process. The oxygen removed some of the carbon from the platinum film; however, the oxygen also increased the deposition rate of the platinum resulting in a film similar to the high temperature deposited film described above. Thus, the conventional methods are unable to achieve both good step coverage and a smooth continuous film, which is especially important in the manufacture of an integrated circuit.
The present invention overcomes the drawbacks of the conventional methods and provides a CVD method that produces a smooth, uniform, continuous film of a platinum group metal that also has good step coverage. The invention includes the addition of nitrous oxide (N2O) and oxygen in combination as a component during the CVD process in order to control the deposition rate of the platinum group metal, which results in a continuous film having good step coverage.
The invention provides a process for depositing a platinum metal on a substrate which includes the steps of flowing a gas having saturated therein a platinum precursor over the substrate at a selected temperature and pressure in the presence of both oxygen (O2) and nitrous oxide (N2O). The selected operating temperature is a temperature at which the platinum group metal deposits on the substrate, but less than a temperature at which the platinum group metal fails to smoothly deposit on the substrate. The pressure at which the process operates is a pressure at which the platinum group metal will deposit on the substrate in a continuous film while maintaining good step coverage. By carrying out this process, a platinum group metal film may be deposited on the exposed portions of the substrate in a uniform film.
The above and other advantages and features of the invention will be more clearly understood from the following detailed description which is provided in connection with the accompanying drawings.